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  • 1
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    Imbricate structure of Luobusa ophiolite, southern Tibet. The 19th Himalaya-Karakorum-Tibet Workshop (2004)
    In:  Himalayan Journal of Sciences, Special Issue, pp. 280, vol. 2
    Details
    Publication Date: 2004
    Keywords: CC 1/1 ; Coordinating Committee ; Himalayas
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    BIBLIOGRAPHY ILP
  • 2
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    Can clay minerals account for the behavior of non-asperity on the subducting plate interface? (2015)
    SpringerOpen
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    Publication Date: 2015-10-15
    Description: Seismicity along the subducting plate interface shows regional variation, which has been explained by the seismic asperity model where large earthquakes occur at strongly coupled patches that are surrounded by weakly coupled regions. This suggests that the subduction plate interface is heterogeneous in terms of frictional properties; however, the mechanism producing the difference between strong and weak couplings remains poorly understood. Here, we propose that the heterogeneity of the fluid pathway and of the spatial distribution of clay minerals plays a key role in the formation of non-asperity at the subducting plate interface. We use laboratory measurements of frictional properties to show that clay minerals on a simulated fault interface are characterized by weak and slow recovery, whereas other materials such as quartz show relatively quick recovery and thereby strong coupling on the fault surface. Aqueous fluids change the mineralogy at the plate interface by producing clay minerals due to hydrate reactions, suggesting that the hydrated weakly coupled regions act as a non-asperity and form a barrier to rupture propagation along the plate boundary at the depths of seismogenic zone.
    Electronic ISSN: 2197-4284
    Topics: Geosciences , Physics
    Published by SpringerOpen
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  • 3
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    Slow stick-slip of antigorite serpentinite under hydrothermal conditions as a possible mechanism for slow earthquakes (2015)
    Wiley
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    Publication Date: 2015-02-01
    Description: ABSTRACT Slow earthquakes, characterised by a different scaling law to regular earthquakes, have been detected at the hydrated plate interface in the subduction zones, but the generating mechanism of them remains almost unexplored. Frictional experiments on antigorite serpentinite under hydrothermal conditions are conducted to assess the distinct scaling law of slow earthquakes. Slow stick–slip was observed at temperatures that were close to the dehydration temperature of antigorite, which is resulted by the localized dehydration of serpentine in the shear zone. The occurrence of slow stick–slip is consistent with the temperature range found in the corner of the mantle wedge in SW Japan and Cascadia, where slow earthquakes occur. The laboratory slow stick–slip show a similar scaling law of slow earthquakes, but distinct from that of regular earthquakes. We propose that the shear-induced dehydration of the serpentine play an important role for the generation of slow earthquakes.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Episodic tremor and slow slip potentially linked to permeability contrasts at the Moho (2012)
    Springer Nature
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    Publication Date: 2012-10-02
    Description: Episodic tremor and slow slip potentially linked to permeability contrasts at the Moho Nature Geoscience 5, 731 (2012). doi:10.1038/ngeo1559 Authors: Ikuo Katayama, Tatsuya Terada, Keishi Okazaki & Wataru Tanikawa Slow earthquakes occur at the plate interface in subduction zones. These low-frequency tremors and slow-slip events are often located at about 30 km depth, near the boundary between the crust and mantle (Moho) on the overriding plate. Slow earthquakes occur on fault patches with extremely low frictional strength. This weakness is generally assumed to result from increased pore-fluid pressures and may be linked to the release of fluids from the descending plate. Here we propose that a contrast in permeability across the Moho results in the accumulation of water and the build-up of pore-fluid pressure at the corner of the mantle wedge that overlies the subducting plate. We use laboratory measurements of permeability to show that gabbroic rock layers in the crust are two orders of magnitude less permeable than serpentinite layers in the underlying hydrated mantle rocks. Inserting our experimental data into a numerical model that simulates pore pressure evolution across the Moho, we show that the pore-fluid pressure at this boundary can be as high as lithostatic pressure. We suggest that water released from the descending plate is trapped at the corner of the mantle wedge owing to this permeability barrier, and then causes the localized slow earthquakes that are triggered by fault instabilities.
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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  • 5
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    Deformation microstructures of glaucophane and lawsonite in experimentally deformed blueschists: Implications for intermediate-depth intraplate earthquakes (2015)
    Wiley
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    Publication Date: 2015-01-17
    Description: A series of simple-shear experiments on blueschist was performed at 400–500°C and 1–2.5 GPa to understand the deformation of seismically active, subducting oceanic crust. The experiments show that brittle microstructures are mainly found at pressures of 1–2 GPa, whereas ductile microstructures form at 2.5 GPa. J -indices (a measure of fabric intensity) of glaucophane crystal preferred orientations change systematically with changing shear strain and confining pressure, and the angle between the slip plane and the shear direction of samples deformed at 〉2 GPa is similar to that of a strain ellipsoid. These results, together with the variable orientations of fine grains in a selected area electron diffraction image at 2 GPa, indicate that the brittle–ductile transition for glaucophane occurs at ~2 GPa. In contrast to this, lawsonite in the experiments show abundant fracturing in most specimens and a poor correlation between the J -index, shear strain, and confining pressure. This demonstrates that lawsonite deformed by brittle failure under all experimental conditions. In the case of a starting material that has a strong fabric and deformed under dry experimental conditions, the brittle–ductile transition zone of glaucophane will be much shallower than 2 GPa. Therefore, our initial experimental results on the deformation behavior of blueschist indirectly support the dehydration embrittlement of subducting oceanic crust (glaucophane) as an important factor in the origin of intraplate earthquakes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Electrical conductivity of magnetite-bearing serpentinite during shear deformation (2012)
    Wiley
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    Publication Date: 2012-10-30
    Description: Electrical conductivity of serpentinite with various amounts of magnetite was measured during shear deformation at high pressure and temperatures (P = 1.0 GPa, T = 750 K) corresponding to mantle wedge conditions to evaluate the contribution of aligned magnetite to the bulk conductivity of serpentinite. Under hydrostatic conditions, the sample conductivity considerably increases when the magnetite volume fraction exceeds 25% in volume, suggesting the presence of the percolation threshold for magnetite interconnection. During shear deformation, the conductivity for the samples with less than 25 vol.% magnetite increased by an order of magnitude or higher with increasing shear strain up to 9, which is likely a result of the clustering or realignment of magnetite grains in the serpentinites. However, activation enthalpy was nearly constant before and after deformation experiments, suggesting that shear deformation is unlikely to enhance establishment of interconnection of magnetite. Consequently, more than 25 vol.% magnetite is needed to establish connectivity of magnetite in serpentinite. On the other hand, the conductivity of serpentinite with low volume fraction of magnetite (5%), which is typical concentration of natural serpentinites, is almost similar to that of magnetite-free serpentinites. The present results show that the interconnection of magnetite in serpentinites by shear deformation is not expected as an origin of the high conductivity anomaly occasionally observed at the slab interface in the mantle wedge. The origin of high conductivity, therefore, indicates the presence of aqueous fluid with high salinity rather than the magnetite interconnection.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Rheological decoupling at the Moho and implication to Venusian tectonics (2014)
    Springer Nature
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    Publication Date: 2014-03-19
    Description: Plate tectonics is largely responsible for material and heat circulation in Earth, but for unknown reasons it does not exist on Venus. The strength of planetary materials is a key control on plate tectonics because physical properties, such as temperature, pressure, stress, and chemical composition, result in strong rheological layering and convection in planetary interiors. Our deformation experiments show that crustal plagioclase is much weaker than mantle olivine at conditions corresponding to the Moho in Venus. Consequently, this strength contrast may produce a mechanical decoupling between the Venusian crust and interior mantle convection. One-dimensional numerical modeling using our experimental data confirms that this large strength contrast at the Moho impedes the surface motion of the Venusian crust and, as such, is an important factor in explaining the absence of plate tectonics on Venus. Scientific Reports 4 doi: 10.1038/srep04403
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 8
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    Corrigendum: Length of intact plasma membrane determines the diffusion properties of cellular water (2016)
    Springer Nature
    Details
    Publication Date: 2016-05-21
    Description: Corrigendum: Length of intact plasma membrane determines the diffusion properties of cellular water Scientific Reports, Published online: 20 May 2016; doi:10.1038/srep25681
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 9
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    Slow earthquakes associated with fault healing on a serpentinized plate interface (2013)
    Springer Nature
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    Publication Date: 2013-05-08
    Description: Slow earthquakes that occur at subduction zones are distinct from regular earthquakes in terms of their slip behavior. We consider this difference to relate to localized hydration reactions at the plate interface that influence the frictional properties. The results of laboratory friction experiments indicate that simulated serpentine faults are characterized by a low healing rate and large slip-weakening distance compared with unaltered dry fault patches. These results are consistent with the slip mechanism of slow earthquakes, indicating that a locally serpentinized plate interface could trigger slow earthquakes, assisted by pore pressure build-up, whereas unaltered dry patches that remain strongly coupled are potential sites of regular earthquakes. Scientific Reports 3 doi: 10.1038/srep01784
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 10
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    Shear-induced permeability anisotropy of simulated serpentinite gouge produced by triaxial deformation experiments (2013)
    Wiley
    Details
    Publication Date: 2013-03-01
    Description: [1]  We have determined the permeability of antigorite serpentinite gouge in three orthogonal directions during frictional experiments using a triaxial gas apparatus, in order to better understand fluid flow in subduction fault zones. The experiments were conducted at room temperature, a confining pressure of 150 MPa, a pore pressure of 100 MPa, and a constant slip rate of 0.58  μ m/s. Although the initial permeabilities are similar in all directions, anisotropy develops during deformation, with the permeability normal to the shear plane becoming one order of magnitude lower than in the other directions when the shear stress reaches steady state. Formation of such permeability anisotropies may enhance fluid flow along the subduction plate interface and serpentinite-bearing fault zones, important in evaluating potentially heterogeneous distribution of fluid pressure along the fault and in understanding the spatio-temporal variation in the seismic activity.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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